1. Field of the Invention
The present invention relates to improvement in an inner periphery driving type rubber crawler having driving protrusions which protrude from an inner face of the crawler.
2. Description of the Related Art
In a conventional structure of a rubber crawler, a plurality of core metals, which are arranged in series along the longitudinal direction of the crawler such that the longer sides of each core metal are in parallel with the width (transverse) direction of the crawler and the center of the core metal is aligned with the center in the transverse direction of the crawler, and a plurality of steel cords surrounding the outer periphery of the core metals, are disposed in a form wherein they are buried in rubber. The central portion of the core metal works as the part which engages with a sprocket (refer to FIG. 17). Therefore, the core metal has a shape in which the thickness increases toward the central portion and the central portion has the largest thickness. This shape markedly increases the weight of the core metal.
Holes to engage with the sprocket are formed between the core metals in combination with the parts to engage with a sprocket. Because of the presence of these holes, steel cords surrounding the core metals are buried in rubber at positions shifted toward both sides in the transverse direction. Therefore, it is necessary that the rubber crawler and the core metal have large widths.
In other words, a conventional structure of a rubber crawler inevitably gives a large weight to the whole crawler and it is difficult to increase the speed and to decrease the weight. Moreover, the driving force is transferred by the contact of the central portion of the core metal and the sprocket and thus the hitting sound generated by the contact of the metals of both parts becomes a major cause of noise. Holes to engage with the sprocket are arranged in a series at the central portion in the transverse direction of the rubber crawler and this causes another problem in that the arrangement of rubber lugs formed at the outer face of the rubber crawler is restricted. There is the possibility of this restriction in rubber lug arrangement becoming a critical point for decreasing vibration during running.
Particularly when a crawler is driven at a high speed, there is the possibility of the above problems of the conventional rubber crawlers causing problems. In order to solve the above problems, an inner periphery driving type rubber crawler is proposed, in which protrusions are formed at the inner face of a crawler at a constant pitch and the driving force is transferred from a sprocket by the engagement of the pins of the sprocket with these protrusions (refer to FIG. 18).
The inner periphery driving type rubber crawler has the advantage in that the crawler has a lighter weight than a conventional one because the crawler of this type generally does not have core metals buried therein and that generated vibration is smaller. Thus, the rubber crawler of this type has a structure more suitable for driving at a high speed than the crawler of the type shown in FIG. 17.
However, the inner periphery driving type rubber crawler has many things to be improved. For example, a driving wheel must have a structure in which the crawler is held down by the wheel at portions in the range of almost the entire width of the crawler because the crawler does not have core metals. Moreover, the driving wheel tends to accumulate dirt because the driving wheel has parts to engage with the driving protrusions.
The conventional inner periphery driving type rubber crawler has the additional problem that the pressure toward the earth in the transverse direction of the crawler cannot be held constant because no core metals are provided and thus a decrease in the pulling power arises and that the probability of wear and chipping of the driving protrusions increases by the contact with the driving wheel made of a metal because the driving protrusions formed at the inner face of the rubber crawler are made of rubber.